Formulation of Soft Serve Ice Cream

There are several ways of obtaining softness in ice cream, and sometimes these may be combined if required. The following techniques are used:

•  Addition of an anti-frost preparation of carbohydrate nature, including MSNF
•  Increase of the overrun
•  Selection of specific emulsifiers/ stabilizers.

 The first is the most important point, and the effect of using freezing point depression factors is discussed below:

i. Lower the Freezing Point

In traditional ice cream there are various ingredients, but not all of them have an influence on the freezing point of ice cream mix

                 Degree of freezing point depression

Fat	: Of no importance
MSNF:	Limited importance (contains lactose and salts)
Sugars	Great importance (give the main effect)
Emulsifier/stabilizer	No importance
Overrun	Great importance

Consequently, the freezing point depression is sought from lactose and salts of MSNF as well as the sugars.

ii Effect of MSNF on Freezing Point Depression

It is known that MSNF consists of approximately 8% minerals, 39% protein and 53% lactose. Lactose is a disaccharide that is in the dissolved state. It lowers the freezing point just like ordinary sugar. The salt content will also have an influence on the freezing point and generally it may be assumed that the MSNF will depress the freezing point to the same extent as a 40-50 DE glucose syrup.

Lactose, is an important part of MSNF, but is only partially soluble. If the MSNF factor (i.e. parts of MSNF per 100 parts of water):

i.e. (%MSNF 100)/ %water

is increased to more than 17, the result will be the risk of a sandy ice cream. By means of enzyme lactase, the lactose may be hydrolyzed into monosaccharides, glucose and galactose which are more soluble and these sugars will lower the freezing point more than the lactose.However, MSNF has a limited effect on the freezing point depression. The main effect is achieved by the sugars, which are present.

iii. Effect of Sugars on Freezing Point Depression

The freezing point of an ice cream mix is first of all dependent on the amount of dissolved solids. The more are the solids dissolved (in the genuine solution), the lower the freezing point. The sugars produce a lowering of the freezing point and it is its molar concentration that determines the freezing point of the ice cream mix.In order to survey the effect of different products, it is necessary to introduce two factors that are related to lowering of the freezing point and the sweetening ability of sugars.

The factors are: Freezing point depression factor (FPDF) and Relative sweetness 

Freezing point depression and relative sweetness of some

sweeteners

In the above table, sucrose was chosen as the datum point and the FPDF and relative sweetness of each sweetener is compared with it.For example, the same amount of dextrose will lead to greater freezing point depression than sucrose due to the difference in molecular weights, and conversely  glucose syrup will produce a less freezing point depression than sucrose. By combining different sweeteners, it is possible to produce desired softness and relative sweetness.Experience has shown that ice cream with FPDF of about 15 will be relatively hard at -18 C and not scoopable, whereas scoopable ice cream should have a FPDF of around 20-25.

A well known and easy way of obtaining scoopable ice cream is to add 2-3% glycerol. The following recipe shows the effect of keeping the total sweetness constant:

Recipe:

Fat                                                       10.0%

MSNF                                                  10.7%

Sucrose                                                11.0%

Glucose solids                                       3.0%

Glycero                                                 l 2.0%

Emulsifier/stabilizer                                 0.7%

Total solids                                         37.4%

Calculation of FPDF and Relative sweetness

sweetness                                FPDF                                                      Relative

Sucrose,                             11% 11 × 1 = 11                                         11 × 1 = 11

Glucose solids,                    3% 3 × 0.8 = 2.4                                        3 × 0.3 = 0.9

Glycerol,                             2% 2 × 3.7 = 7.4                                        2 × 0.8 = 1.6

                                                             20.8                                                       13.5

The addition of 2% glycerol produces a FPDF of 20.8 which will be sufficient to give the product scoopable properties.

The effect of other combinations can be considered, especially if a combination of saccharides can be used to produce acceptable softness and sweetness in the final product. A recipe which can be considered without the use of glycerol is shown below:

Recipe:

Fat                                                10.0%

MSNF                                          10.6%

Sucrose                                         4.5%

High fructose corn solids                6.0%

Glucose solids                                2.0%

Dextrose                                        4.5%

Emulsifier/stabilizer                         0.7%

Total solids                                    37.3%

Calculation of FPDF and Relative sweetness

	FPDF	Relative sweetness
Sucrose, 4.5%	4.5 × 1 = 4.5	4.5 × 1 = 4.5
Glucose solids, 2%	2 × 0.8 = 1.6	2 × 0.3 = 0.6
High fructose corn solids, 5%	5 × 1.8 = 9.0	5 x 1 = 5.0
Dextrose, 4.5%	4.5 × 1.9 = 8.6	4.5 × 0.8 = 3.6
	23.7	13.7

The correct choice of saccharides can make it possible to produce a scoopable ice cream with the same solids and total sweetness as that of regular ice cream.